BULLETIN 341 REPRINTED JUNE 1940 INSECTS INFESTING STORED FOODS HAROLD H. SHEPARD UNIVERSITY OF MINNESOTA AGRICULTURAL EXPERIMENT STATION CONTENTS Page Flour-milling problems 4 Breakfast foods 5 Bakers' problems 6 Miscellaneous cereal products ... 6 Foods high in fat and protein .. 7 Miscellaneous foods 7 Foods in the horne .... 7 Life history of a typical stored-food insect 8 Descriptions of the principal insects infesting stored foods..... .... ......................... 9 Structure of a typical insect.... 9 Confused flour beetle, Tribolium confusum.. ........................................ ........................ 10 Red flour beetle, Tribolium castaneum ... 12 Saw-toothed grain beetle, Oryzaephilus surinamensis............. 13 Flat grain beetle, Laemophloeus mimtfus ... ......................... 14 Cadelle, Tenebroides mauritanicus ......... ................ ........ ....................... 14 Yellow meal worm, Tenebrio molitor... IS Dark meal worm, Tenebrio obscurus .... 15 Mediterranean flour moth, Ephestia l~iihniella........ 16 Indian-meal moth, Plodia iuterpuncte/la... 18 Meal snout moth, Pyralis farina/is.... 18 Rice moth, Corcyra cephalonica........ 19 Grain weevils ................................. 19 Drugstore beetle, Stegobium paniceum.. 20 Cigarette beetle, Lasiodenna serricorne 20 White-marked spider beetle, Ptinus fur. 21 Hairy spider beetle, Pti11us villiger.. 21 Dermestid beetles ............ ............... .... 23 Square-necked grain beetle, Silvanus gemellatus = Cathartus quadn'collis 24 Foreign grain beetle, Ahasverus advena.. .... .... ........... ...... 24 Black fungus beetle, Alphitobius piceus .. 25 Two-banded fungus beetle, Alphitophagus bifasciatus... 25 Broad-horned flour beetle, Gnathocents cornutus.. .. .............. .. 25 Slender-horned flour beetle, Gnathacerus maxillosus... 25 Small-eyed flour beetle, Palorus ratzeburgi. ... 26 Long-headed flour beetle, Lathetiws aryzae.... 26 Red-legged ham beetle, N ecrobia rufipes... 26 Vinegar fly, Drosophila ampelophila .. 27 Cheese skipper, Piophila casei.... 27 Psocids or book lice .... 27 Mites 28 Miscellaneous insect pests .. 29 Control of insects in store~ food products . 29 High temperature 30 Low temperature 34 Contact sprays 34 Fumigation 35 Literature 39 Insects Infesting Stored Foods 1 HAROLD H. Sr-rEPARD2 HIS BULLETIN contains information on the biology and control T of the common insect pests of flour and other ground or processed cereals, dried fruits, dried-milk products, cured meats, nuts and their products, various spices, and many other foods that undergo some manu­ facturing process and subsequent storage. The pests of whole grain and other seeds have been discussed in a separate bulletin. Such household pests as cockroaches, ants, flies, and silverfish, common elsewhere in stored products, are discussed in separate circulars. Because of their short storage period, most fresh foods such as fruits and vegetables, do not become infested except by those field insects that remain on them after harvesting. It is not pleasant to think of eating food upon which insects have been crawling and feeding. Although such food is usually considered un­ clean, and most people will not eat it if they know of its condition, if the insects are not germ carriers there is no evidence that it is at all in­ jurious. The greatest damage to food by insects is not the amount actually eaten but that which is rendered unfit or undesirable for human consumption by the mere presence of the insects. In some cases an entire business has been ruined because the buying public found insects in its products. If one includes the insect damage to stored grains, it is likely that the total annual loss of stored food products, from the beginning of storage at harvest to the time of home consumption, amounts to nearly a half billion dollars in the United States alone. The large amounts of food thrown away or requiring reconditioning result in losses that could for the most part be prevented at little cost. Carelessness, lack of attention to details, and lack of information regarding a few simple entomological facts are responsible for most of such losses. If the following information is studied and the suggestions are followed, it should be relatively easy to overcome these obstacles, either in food-processing establishments or in the home. 'Accepted for publication November 10, 1938. 2 In 1921 the :Minnesota Agricultural Experiment Station published Bulletin 198, "Insects Infesting Stored Food Products," by Royal N. Chapman. This bulletin we.s slightly revised in 1932 by the author of the present bulletin. Instead of again reprinting Bulletin 198, the subject matter has been largely rewritten and brought up to date where necessary. The author, however, has drawn heavily from the original work of Dr. Chapman and wishes by this note to indicate his indebtedness for that assistance. 4 MINNESOTA BULLETIN 341 FLOUR-MILLING PROBLEMS Retail customers often blame the miller for the presence of insects in flour and other ground cereals although the source of the difficulty is in the wholesale or the retail grocery. The best proof of innocence the miller can produce is an establishment free from insects. The volume of business, the construction of the buildings, and the amount of dust constantly accumulating make the flour mill a favorable place for insects and a difficult place in which to combat them. So far as milled products are concerned, the miller is near the source of insects compared to the various dealers who pass these products on to the consumer. Although none of the insects that attack the raw material-the unmilled grain--do any extensive damage to the milled products, it is important to distinguish between the insects that attack the sound grain and those that follow them as secondary pests in the damaged grain. These secondary pests also work in the milled products. The insects that attack the sound grain "grind" it, and the material left is much like that which comes from a mill so far as the ability of other insects to attack it is concerned. It is of the greatest importance that the miller should realize fully the hazard involved in buying grain that has been damaged to any extent by insects. It may contain some of the secondary insects that become primarY. pests of the milled products. Insects that live in mills are confined largely to the elevators and mills or the warehouses and stores through which the milled products pass on their way to the consumer. They are passed from one mill to another in empty sacks that are exchanged or returned. Because insect eggs are not easily seen, sacks may be thought to be free from insects although they contain hundreds of eggs that will hatch in a few days. An ordinary cleaning of the sacks may remove all the insects but leave the eggs. The only safe method is to fumigate or heat sacks when they are returned and before they are brought into the mill. A little time spent in such treatment will save much time in trying to rid the mill of the insects once they have entered. Leaky, badly patched sacks are likely to promote infestation of the flour ; neat, tight sacks help to prevent infestation as well as to give a good impression of the product. For the sake of his own business, the miller must watch the products that go out so that they may not endanger the business of his customers. Not only should his packaging be carefully done to prevent leakage and subsequent infestation, but the cars and trucks for transporting his goods should be cleaned thoroughly before loading. However, the extent to which flour is infested while in transit is often overestimated. The time involved, a week or less, is too short for insects to develop throughout the shipment. Ordinarily relatively few adult insects vvill migrate to the sacks ; those that do are found mostly in the sacks near the walls of the railroad car. Cotton and Wagner ( 1938) list several ways by which a flour mill may become infested: 1. Insects entering with the grain stream. 2. In- INSECTS INFESTING STORED FOODS 5 sects from infested clear or low-grade flour used in blending operations. 3. Insects from infested flours returned to the mill from grocers' ware­ houses and elsewhere. 4. Insects in returned bags. 5. Insects in second­ hand machinery purchased for installation in the plant. 6. Insects from infested feeds stored in the mill. A study of the species of insects occurring in the mill streams of flour mills in Kansas, Oklahoma, and Missouri showed Tribolium comprised 84.65 per cent of all the insects taken, Laemophloeus 7.95 per cent, and Tenebroides 3.16 per cent (according to Good, 1937). More than 25 species were found in the remaining 4.24 per cent. "The low-grade flour elevator boot showed the highest average population, with three of the middlings elevator boots, the fourth, second, and fifth, next in order. ... The high population in the low-grade flour elevator boot is probably due to the position that the low-grade-flour stream occupies in the milling system and the inability to redress such flour properly, coupled with its greater palatability to insects." (Good, 1937.) A recent development in milling practice has been the installation of redressing machinery for the removal of foreign material that has been accidentally incorporated in the flour during the process of manufacture. If a fine enough bolting cloth is used, all stages of insect life can also be removed by this process. The machinery must be so constructed and located as to eliminate any chance for insect infestation to contaminate the flour between the time it passes through the cloth and the time it reaches the packer bins. Reels, because of their construction, are undesirable for this purpose. The conveyors in the reels are so arranged that it is a simple matter for insects removed in the redressing process to crawl over into the conveyor that handles the finished flour. Because sifters are so constructed that the tail over and finished flour are handled by separate spouts having no connection, they should be used instead of reels.